FR2506471A1 - Stereoscopic film and slide projector - has opaque side screens in optical path to eliminate window effect - Google Patents

Abstract

The slide or film projector has two sections which give two superimposed images from a stereoscopic pair. Interference from the inner edges of the slide frame leading to stereoscopic window effects are eliminated. Each projector lamp (1) shines through a condenser (2) and the slide (3) and through a polarising filter (6). Passing the objective (4), the images meet on a screen (5). Opaque screens (7,11) with saw tooth edges cooperate with others (12) with specially treated edges. Both screen sets are at the sides of the projector optical axis and help to eliminate the window effects.

Description

 The present invention relates to projection systems of slides or filas restoring the relief within a dual image displayed on a screen.

 The known device uses two projectors in which is introduced the stereoscopic pair, that is, for example, two slides, one intended to be seen by the left eye, the other by the right eye. In order to sort the images, the two projectors are each equipped with a polarizing filter whose axes are crossed. Each spectator wears glasses also equipped with crossed polarizing filters, while the metallized screen preserves the plane of initial vibration of the beams. Thus, the image of each of the two slides reaches, and only it, the eye which is intended for it, the fusion of the two restoring a striking vision of the relief, in three dimensions.

 But the vertical edges of the two shots themselves produce an image that frames the entire composition: 1 'window effect. The latter is, for two reasons, particularly troublesome. Any scene located behind the window is isolated by the latter, causing an inevitable effect of separation, remoteness, strongly opposing the visual and psychological integration of the viewer. Any inage restituted in front of the window is seen, on the other hand, struck with an irreversible visual disturbance along each of the vertical edges of this one. The advanced parts of the image are sliced, cut in an aggressive, unreal way; the vision is then very uncomfortable and the local restitution of the relief, impossible.

 The device according to the invention makes it possible to overcome this double obstacle by eliminating the window effect. He uses a known installation of slide projection or cinematographic film. This forms on a ream projection screen the two simultaneous and superimposed images of a stereoscopic pair.

Thus two projectors are used in parallel, or the two beams of a single projector equipped with a dual optics.

 The device according to the invention is firstly characterized by the ease of use, on each of the two beams, of means that can act alone or combine with each other, and whose purpose is to intercept or suppress the image of the edges. at least vertical, the frame of the slide, or the limit of the cliche dream, or the mechanical window delimiting the image beam of a cinema projector, while also modifying the imagery from the marginal zones of the photographic emulsion, become transition zones between the primitive image, conserved towards the center, and the external parts where the image no longer exists.

 This modification of the imagery is to be considered obviously from the point of view of the observer, at the end of the light path, ie after the contact of the beams with projection screen.

Therefore, the means of the invention intervene both in the projectors at the level of this screen. In general, moreover, they can be used both individually and in association, variously combined with each other.

 Thus, there is no more image of the inner vertical edges of the frames in the strict sense, nor a sudden stop of the stereoscopic image at its edges, which would be the same. The marginal transition zone alone now circumscribes the stereoscopic image in a happy way. We realized the nodification or even better, the removal of the "window".

 The invention is further characterized by the specific means for restoring a stereoscopic pair. The two light beams are thus polarized by virtue of the interposition of at least one polarizing filter on each beam, preferably born of a non-elastic gap, between the lamp and the emulsion, just before the latter. A projection screen, operating by reflection, or retro-projection by transmission, receives the double image and retains, for example stil is "metallized", the final polarization of each of the two beams. It presents, in the case of a linear polarization, the respective crossed axes. Finally, each spectator observes the image in three dimensions through polarizing filters, also crossed so as to judiciously sort the two basic images. to present to the proper eye.

These filters are either arranged on glasses, individual or bridged on fixed supports accessible to everyone, or presented alternating strips with crossed axes through glazing integrated into obserration panels, or still used in any other way, the present enumeration is not, in the context of the invention, limiting.

 Equally, the use of circular polarization filters, or elliptical, with direction of rotation inverted, or more than one linear polarization filter, on each of the two beams, not including the filters specific to the observation means arranged at spectators, although not immediately justified, would remain within the framework of the deans of the invention.

 To explain the rest of the description, we will agree to distinguish between the "projection screen", so called indifferently according to whether it functions by reflection or transmission, and "optical screens, 11 opaque surface elements, or semi- transparencies, or transparencies, of uniform or non-uniform optical density, placed at suitable points in the path of the light beams.

 According to an advantageous embodiment of the invention, there is produced on each of the two beams a wide, continuous and progressive gradient of each image at its edges, until the suppression of light in the outer parts, by various means, and in particular by interposition of opaque optical optics rectilinear or slightly curved arranged in pairs, at least along the vertical portions, at the edges of the respective beams. These screens are placed, in a nonlimiting manner, preferably at some distance from the plane of the emulsion, slide or film, between the latter and the lens, or even if necessary between the lens and the projection screen. The highly defocused image of the optical screens is superimposed on that of the projected and developed snapshot.

By an effective diaphragmation in cat's eye, one quickly modifies the image resulting from the latter in its edges. It causes, although it remains clear, a progressive fading of the stereoscopic image into an extended shading where the recognition of a "window" is impossible. Any visual embarrassment then, disappears.

 It is important that the optical screens are provided with profiled edges in a variable manner, in order to control at will the photometric curve of the marginal gradient of the image. The means of intention thus include, as non-imperative and nonlimiting examples, screens with linear edges, straight or curved, as well as screens cut at their edges along small teeth. triangular, small undulations, see furnished with a row of small bristles glued brush style etc ... We can also use with interest semi-transparent optical screens arranged alone or in combination with the previous ones, of uniform optical density or no, and possibly hatched or screened.

 In general, any appropriate use or combination of one or more optical screens of any kind and of any structure and any size, placed in any places at the edge of the beams and contributing to the modification of the imagery marginal areas of the photographic emulsion remains in the field of the invention. Singularly, the realization of a juxtaposition in the same plane crossed by the ase of the ones, elongated elements of optical screens preferably vertical and nature or different structures, belongs to the means of the invention.

 Another convenient embodiment of the latter employs one or more surfaces, traversed by the ensesble of the beam concerned, central parts of the included image, and of non-uniform optical density. Differential absorptions then produce the desired effect on the images.

 In this connection, it would still be in the field of the intention to use a coordinated variation of the optical density of the emulsion itself of each of the two components of the stereoscopic pair, to obtain equivalent results.

 Finally, in the case of movie projectors, the means used in the context of the invention could include the removal of the mechanical window liniting the edges of the light beam from the film, in order to possibly make a more effective intervention. on the edges of the images.

The theory of stereoscopic restitution shows that it would be necessary for each width to have a width 1 of the transition zone thus produced equal to or greater than twice the largest difference on the screen of the homologous points of the two projected images. But in practice, one can admit, to the extreme rigor
H and V being the horizontal and vertical dimensions of the image, a minimum value of 1, such that # H x (3.V), with (3.V) = 1
40 2H in size 24 x 36 mi.

 This transition zone ideally presents, as a non-imperative or limiting example, from the inside to the outside, first a threshold, a discrete value but visible to the eye, a shadow border announcing the gradient which continues in adjacent parts; then, a wide zOne decreasing luminance in a fairly fast slope, possibly a plateau; finally, an extinction edge, without too fast breaking, preferably evanescent.

 We will situate, in coherence with the practical experimentation, the inner limit of this marginal transition range of the edges of one of the images, on the screen of projection, and during the development, in coincidence with the photometric band whose luminance, when a photographic emulsion of uniform optical density is projected over its entire surface, and measurements in the axis of the beams, is equal, on a projection screen, to fourteen hundredths of the luminance at a point to the left or to the right, halfway between the center and the edge of the nearest left or right screen, on the one hand, and halfway between the upper and lower edges, On the other hand, it is convenient to have a photometer equipped with a slit: placed against the projection screen, the sensitive cell receives the light directly from the projector, or the slot is placed in the focal plane of a focal length lens s uffisante, forming the image of the screen. The outer limit of the transition range is that which corresponds to the total disappearance of any light emanating from the photographic emulsion, diffusion in the objectives excepted.

 According to another type of embodiment, particularly interesting, it has on the edges, at least vertical, and at the right on one of the two beams on the right edge, on the one hand, left on the other hand, birefringent blades Intercepting only a small part of each beam and therefore the image. These blades, or blades, are necessarily placed between a polarizing filter and the screen. Advantageously, for example, cellophane sheets or even mica strips are used. These birefringent elements cause the formation of elliptical polarized light, see circular, or even the appropriate rotation of the linear polarization axis if they ideally constitute a half-wave plate. Thus, on the edges of the image, the polarization light no longer conforms to the spatial arrangement required for the eye-sorting of images, through the glasses, as obtained in the center. A part of the corresponding beam of the left image reaches the right eye, and if necessary, inversely. It follows, on the edges, a suppression, or a strong attenuation of the stereoscopic effect. In marginal zones, the relief collapses, the image flattens out, at least in part, and the effect of the window is thus eliminated. By the center, we observe, as long as we take care to defocus the image of the birefringent blades, by moving them away from the plane of the emulsion, a progressive recovery of the three-dimensional structure of the image developed, the whole being of a happy effect if the transition is not too broad, particularly well accepted visually.

 It is advantageous to provide, in the context of this embodiment, a partial or progressive absorption towards the edges of the parts of the beam intercepted by the birefringent elements.

For this purpose, it is easy to achieve a combination of the means of the invention previously exposed. The birefringent blades can also be repositioned by linear or circular polarization filter elements, or associated with these elements. The technical result obtained remains generally valid, provided that the orientation of the filters is correct: change of the polarization state of the beams at their edges only and possible controlled absorption of the light passing through them.

 Finally, it will be possible to act on the geometrical arrangement of the various means of the invention so as to conceal at best the parts of each of the two images which, due to parallax, are not common between the edges and in their first planes. they. Left image elements that are not seen by the right eye, create a visual disturbance, and vice versa. FIGS. 6 to 8 will be used in order to produce the standard contour images represented, which are not limiting and can be combined, by progressive horizontal translations from the vertical, of the left limit of the left beam, on the one hand , from the right boundary of the right one, on the other hand, zero at the top, of maximum value xg and xd at the bottom, progressing from the top to the bottom, and such that xg = xd.

 The device according to the invention also comprises, secondly, and in order to amplify the results already obtained, means for causing at the projection projection screen or transmission back projection, in its peripheral parts and at least on the vertical edges, a progressive marginal transition zone opposing the existence of a sharp boundary separating the light range of the absorbent or unlit external parts. This limit, when it is placed at the edges of the image, even if the latter extends to the right and left beyond the screen, constitutes or reconstitutes itself, in fact, a stereoscopic window presenting the same disadvantages as when the window is caused by the frames of a stereoscopic couple of slides.

 This zone on the projection screen will, of course, obey quantified criteria comparable to those defined above for the marginal gradient of the image. In practice, it would be sufficient for H '3 V' to be so wide that the> 80 x 2.H ', V' and H 'are the vertical and horizontal dimensions of the screen. This means may be used optionally alone, without departing from the scope of the invention, or preferably in combination with the other means listed. It will also preferable, a gradual extinction of the image, going from the center to the outside, in the marginal zones. Advantageously but not limitatively, it will be obtained by providing an absorbent layer of varying thickness or density. A matte paint, preferably black, is ideally suited. The integration of elementary structural inequalities may contribute to the progressivity of light absorption. Thus, the realization of a frame, or scratches, between it for example within the scope of the invention.

on the other hand, it can be envisaged to intervene not on the screen itself and but at a surface placed between the screen and the projectors, for example by arranging the absorbent means on a transparent plate, or elements plate, in contact or at some distance from the projection screen. Polarizing elements, see birefringents, absorbing or modifying the stereoscopic restitution, belong in this context to the means of the invention.

Any combination of the means described may allow to harmoniously contribute to the goal pursued. For example, it is possible to combine elements of birefringent blades and optical screens, surfaces covering the entire beam, of uniform or non-uniform optical density, profiled screens acting as diaphragms, while respecting or not respecting the provisions of FIGS. 8. Furthermore, each of the transparent or semitransparent elements mentioned allow, through their polished entry and exit faces, an optical transition that respects the geometrical formation of the images. Although they are not a priori desirable, however, transparent or semitransparent transparent elements may be integral parts of the means of the invention.

The attached drawings, given by way of non-limiting examples, include, on plates 1 and 2:
- Figure 1, a preferred embodiment described below.

 - Figure 2, the illustration of the advantageous optical screen structure. In (a), profiled sawtooth edges; in b), corrugated edges; in c), composite edges, successively joining together: opaque structure - moderately absorbing - weakly absorbing; in edges trimmed with similar "brushed" bristles.

 - Figure 3, typical photometric curve obtained as an example after contact beams on the projection screen, when projecting a slide of uniform optical density. In (14), value of the luminance at the reference point, in (15) practical internal limit of the gradient, in (16), external limit.

 - Figure 4, arrangement of bi-refractive blades (18) in the vicinity of the emulsion (17), and absorbing optical screens (19), after a polarizing filter (20).

 FIG. 5, orientation of a polarizing filter (21) and a half wave wave (22): Angle of 22 5 of the neutral lines of (22) and of the polarization axis, causing a rotation of 45.degree. this last.

 FIGS. 6 to 8, profile on the projection screen of the contours in G and D of the left (left) and right images, obscuring in the stereoscopic pair most of the parts of images which, because of the parallax, are not common to each other.

 They show how to generally dispose of all the means of the invention in order to obtain the outlines of images presented. In Figure 6, without special intervention, the point (23) of the image would be seen by the left eye, but not by the right, and conversely for the point (26). After intervention according to the invention each of the points (23) and (26) are entirely invisible and only the points (24) and (25) are, in the margin of the image, visible and visible from both eyes. The visual comfort is then complete and all the harmful aspects of the old window effect are eliminated.

 With reference to FIG. 1, one of the variants according to the invention comprises two slide projectors respectively creating the beams received on the left, by the left eye, and symmetrically. On each of these, the lamp (1) forms on the screen of the condenser (2) and the lens (4) an image on the screen (5) of the slide (3). A polarizing filter (6) is arranged between (2) and (3), the axes being crossed respectively. The screen (5) is calibrated. We observe through glasses not shown and equipped for the left and right eyes polarizing filters parallel to the respective filters (6). In (7), two pairs of opaque opaque screens (11) metal sawtooth edges according to Figure 2a) are arranged vertically at the edge of the beams. They are associated with two other pairs of screens (12) made according to Figure 2c) and photographically framed according to two ranges of different densities but uniform. The dimension (8) is equal to 19.5 mm. and the dimension (9), 33 mm. for a goal of 90 mi. open at F / 2.5, diaphragmed at (10) by a 21 mm square diaphragm. side circumscribing the double image of the filament formed at this location by (2) and (4).

On the periphery of the projection screen (5) are arranged, against the latter, two vertical wide blades (13) of transparent matt transparent plastic sheet lined with a non-uniform black-absorbent weft providing a gradual absorption towards the outside and complete at the edge of the screen. The horizontal boundaries themselves have a narrow gradient.

 The projection device thus described allows the reproduction without any hindrance of any part of the image in front of the screen. It offers new and expanded possibilities of special stereoscopic effects, such as daring gushing effects to spectators, or large overflows of images in the room.

It contributes particularly clearly to a very good psycho-visual integration of the relief, in all its manifestations, even unusual, in the absence of a "window" whose presence remained a perpetual embarrassment. Visual comfort is greatly increased. The invention will therefore find a very advantageous use whenever audio-visual projections stereoscopy, whatever their content.

Claims (10)

 1. Projection device for slides or cinema film having two beams forming simultaneously and superimposed, the two images of a stereoscopic pair, characterized in that it comprises firstly, on each beam, means realizing first the interception or suppression of the image of the internal edges of the frame of the slide, or the edges of the plate itself, or the mechanical window defining the beam from a movie film, including the possible removal of this last, and second, the modification of the imagery from the marginal zones of the photographic emulsion and considered after the contact of the beams with the projection screen, realizing a transition zone at the edge of the image, at least in its vertical parts, modifying or eliminating the stereoscopic window effect, and secondly, means including in the path of each beam at least one polarizing and provoking filter a final polarization of the respective beams which has either crossed linear polarization axes or an inverted direction of rotation, means for observing through polarizing filters, and a screen retaining by reflection or transmission the beam polarization.  2. Projection device according to claim 1, characterized in that it produces a marginal gradient of each of the two images projected and focused, continuous and progressive, such as its width on the projection screen, measured with a slit photometer and in the beam axis, from the photometric band whose luminance, when a photographic emulsion of uniform optical density is projected, is equal to fourteen hundredths of the luminance at the points situated at half height and at equal distances from the center and the vertical edges of the projection screen, to the band where the total extinction of the image is reached, at least equal to the value 1 = 40 x (-2.YH), V and H being the vertical and horizontal dimensions of the image.  3. Projection device according to claim 2, characterized in that the means comprise a set of at least two pairs of optical screens arranged in pairs on the respective edges of the two light beams and structures not sacecently sacramentally homogeneous .  4. projection device according to claim 2, characterized in that the means comprise on each beam at least one surface through which the light and non-uniform optical density.  5. Projection device according to claim 2, characterized in that the means comprise a coordinated variation of the optical density of the two photographic emulsions including the projected images.  Projection device according to claim 1, characterized in that the means producing the image boundary transition zone comprise birefringent plate elements or linear or circular polarizing filter elements placed between a polarizing filter and the screen.  7. Projection device according to claim 6, characterized by deans achieving light absorption for the beam portions passing through the birefringent blades.  8. Device according to claims 1 to 7, characterized in that the respective contours of each image are projecting so as to progressively from top to bottom and with respect to the vertical, in accordance with Figures 6 to 8, a horizontal translation interesting the left limit of the beam intended for the left eye, of zero value at the upper part of the projected image and of the maximum value xg at the lower part, and a translation xd of interest to the right limit of the beam intended for the right eye, such that xg = xd.  9. projection device according to claims 1 to 8 characterized by means disposed at the projection screen or retro-projection and realizing after integration of the elemental inequalities of structure, a progressive marginal transition zone, since the full reflection range or light transmission up to a maximum absorption area at the edges of the screen, of width at least equal to 1 '= H' (3 V '), V' and H 'being the dimensions vertical and horizontal of the screen  10. Projection device according to claim 9, characterized in that the means producing the transition zbne on the screen comprise an absorbent thin layer of non-uniform thickness or density.